One operation frequently employed in the production of semiconductors is an etching operation. In an etching operation, one or more materials are partly or wholly removed from a partially fabricated integrated circuit. Plasma etching is often used, especially where the geometries involved are small, high aspect ratios are used, or precise pattern transfer is needed.
Typically, a plasma contains electrons, as well as positive and negative ions, and some radicals. The radicals, positive ions, and negative ions interact with a substrate to etch features, surfaces and materials on the substrate.
With the move from planar to 3D transistor structures (e.g., FinFET gate structures for logic devices) and advanced memory structures such as Magnetoresistive Random Access Memory (MRAM), plasma etching processes need to be increasingly precise and uniform in order to produce quality products. One problem with conventional etching techniques is that etching byproducts, instead of being swept away, are sometimes re-deposited on surfaces where such deposition is not desired. For example, the byproducts may deposit back on the substrate, where they interfere with further etching, or on the etching apparatus. In many cases, the etch byproducts that are re-deposited are dissociation products of other etching byproducts.
Unwanted deposition on the substrate can cause many problems including poor etch results (e.g., a non-vertical etching profile, etching non-uniformities, etc.) and sub-standard substrates (e.g., the unwanted deposition may form a short in an etched stack). Unwanted deposition on the apparatus can cause additional problems including an increased need for cleaning, shorter apparatus lifespans, and less efficient operation of the apparatus.
Thus, there exists a need for improved semiconductor fabrication methods and apparatus which prevent re-deposition of byproducts during etching.